EP 0 575 301 B1 describes a pneumatic power tool having such a speed control device, named speed governor, which comprises a valve element and is ranged to control the pressure air flow as a response to a speed responsive control pressure.
In the previously known device, the speed governor has an air inlet flow control valve which is activated by a control pressure derived from the motive air flow. The output air from the speed governor valve unit of EP 0 575 301 B1 follows a passage inside the housing of the power tool through a feed passage so as to reach a plurality of nozzles. The valve element is balanced between a control pressure and inlet air pressure such that the air feed flow to the nozzles is sufficient to maintain the turbine wheel rotation speed at a desired level.
The power tool according to the background art works well, but a recent demand has raised requests for operational economy and in particular higher energy efficiency.